PM: Run the driver callback directly if the subsystem one is not there

breaks suspend for his libertas wifi, because SDIO has a protocolwhere the suspend method can return -ENOSYS and this means "There isno point in suspending, just turn me off". Moreover, the suspendmethods provided by SDIO drivers are not supposed to be called bythe PM core or bus-level suspend routines (which aren't presend forSDIO). Instead, when the SDIO core gets to suspend the device'sancestor, it calls the device driver's suspend function, catches theENOSYS, and turns the device off.

The commit above breaks the SDIO core's assumption that the devicedrivers' callbacks won't be executed if it doesn't provide anybus-level callbacks. If fact, however, this assumption has neverbeen really satisfied, because device class or device type suspendmight very well use the driver's callback even without that commit.

The simplest way to address this problem is to make the SDIO coretell the PM core to ignore driver callbacks, for example by providingno-operation suspend/resume callbacks at the bus level for it,which is implemented by this change.